Eureka, California Coastal Digital Elevation Model

Perspective view of DEM

NOAA's National Geophysical Data Center (NGDC) is building high-resolution digital
elevation models (DEMs) for select U.S. coastal regions. These integrated bathymetric-topographic
DEMs are used to support tsunami forecasting and warning efforts at the NOAA Center
for Tsunami Research, Pacific Marine Environmental Laboratory (PMEL). The DEMs are
part of the tsunami forecast system SIFT (Short-term Inundation Forecasting for Tsunamis)
currently being developed by PMEL for the NOAA Tsunami Warning Centers, and are used
in the MOST (Method of Splitting Tsunami) model developed by PMEL to simulate tsunami
generation, propagation, and inundation. Bathymetric, topographic, and shoreline data
used in DEM compilation are obtained from various sources, including NGDC, the U.S.
National Ocean Service (NOS), the U.S. Geological Survey (USGS), the U.S. Army Corps
of Engineers (USACE), the Federal Emergency Management Agency (FEMA), and other federal,
state, and local government agencies, academic institutions, and private companies.
DEMs are referenced to a variety of vertical datums and horizontal datum of World
Geodetic System of 1984 (WGS84). Cell size for the DEMs ranges from 1/3 arc-second
(~10 meters) to 3 arc-seconds (~90 meters).

Developed for the Pacific Marine Environmental Laboratory (PMEL), NOAA Center for
Tsunami Research program in support of NOAA's tsunami forecasting and warning efforts.

Use Limitations

Not to be used for navigation. Although these data are of high quality and useful
for planning and modeling purposes, they are not suitable for navigation. For navigation,
please refer to the NOS nautical chart series.

Produced by the NOAA National Geophysical Data Center. Not subject to copyright protection
within the United States.

While every effort has been made to ensure that these data are accurate and reliable
within the limits of the current state of the art, NOAA cannot assume liability for
any damages caused by any errors or omissions in the data, nor as a result of the
failure of the data to function on a particular system. NOAA makes no warranty, expressed
or implied, nor does the fact of distribution constitute such a warranty.

All datasets obtained by NGDC were converted to common horizontal and vertical datums
of NAD 83 geographic and NAVD 88, respectively, using FME and VDatum tool. They were
also converted to common file format, ESRI point shapefiles, for visualization and
inspection.

Datasets were visually inspected with ArcGIS for identification and editing of data
anomalies. Datasets were then compared with overlapping datasets to ensure data consistency.

Coastline datasets were merged and adjusted to fit satellite imagery.

xyz files of the bathymetric data were surfaced using GMT's 'surface' tool onto a
1 arc-second grid outside Humboldt Bay and 1/3 arc-second inside the bay that interpolated
to fill empty cells. Points extracted every 10 meters along the coastline were also
included to ensure that the bathymetric grid reached zero at the coast. The resulting
Arc ASCII grid was imported into ArcGIS and clipped to the coastline to remove values
over land.

xyz files for each input dataset were gridded using MB-System's 'mbgrid' tool, which
utilizes a high-tension spline interpolation method to fill grid cells with no input
elevation values. Preferential weighting was given to more recent, higher-accuracy
datasets. Gridding was performed in quadrants, each with a 5% data buffer. The grids
were imported in ArcGIS and seamlessly merged to create the NAVD 88 DEM.

The NAVD 88 was quantitatively evaluated by comparing with source datasets and with
elevation values extracted from NGS geodetic monuments. It was visually evaluated
by converting to UTM-zone coordinates (units of meters horizontally and vertically)
and then creating a slope grid to identify gridding artifacts in the NAVD 88 DEM.

A conversion grid that models the relationship between NAVD 88 and MHW was created
using data points and the VDatum transformation tool. This conversion grid was added
to the NAVD 88 DEM to generate the MHW DEM.

The MHW DEM was qualitativley evaluated by comparing with nautical charts and onsite.